Question

If x2 + ax + b = (x – 9)(x + 9), what is the value of

ab?
A) -81
B)
0
C)
81
D) 1458​

Answer 1

B) 0

Explanation:

x² + ax + b = (x – 9)(x + 9)

x² + ax + b = x² – 9x + 9x – 81

x² + ax + b = x² + 0x – 81

x²=x² +ax = +0x +b = -81

a = 0 b = -81

ab = 0(-81) = 0

Answer 2

Explanation:

X2+ax+b=(x-9)(x+9)

X2+ax+b=x2-9x+9x-81

X2+ax+b=x2-81

therefore,a=0,b=(-81)

Then , ab = 0×-81 = 0